1. Field of the Invention
The present invention relates to a shaft bearing structure of spindle motor capable for a laser beam printer (hereinafter referred to as LBP) or an optical disc drive.
2. Description of the Related Art
A laser beam printer (hereinafter referred to as LBP) is capable of high speed printing, so that the use of such an LBP is increasing especially in business field.
As the recent LBP complies with color printing, a spindle motor for LBP is required to stably rotate in high speed. In other words, the spindle motor for LBP is required to have a shaft bearing which provides stable rotation in high speed.
FIG. 1 is a diagram for explaining a structure and operation of a LBP. In FIG. 1, a LBP xe2x80x9cAxe2x80x9d is composed of a semiconductor laser driver 100 controlled by an external equipment (such as a computer) 101 through a controller 102 and a DC controller 103, a scanner motor driver 104 controlled by the DC controller 103, a cylindrical lens 105 to pass a laser beam emitted from a semiconductor laser controlled by the semiconductor laser driver 100, a polygon mirror 106 attached to a spindle motor (not shown) of which rotation is controlled by the motor driver 104 by the controller 103 to reflect the laser beam emitted through the cylindrical lens 105, a spherical lens 107 and a toric lens 108 for spreading the laser beam onto a photosensitive unit 109 for printing information onto a sheet of paper not shown, a horizontal synchronizing mirror 110 and a BD lens 111 for monitoring the laser beam through an optical fiber 112 for feedback control.
The polygon mirror 106 has four to six sides and is maintained at the rotational velocity of 20,000 to 30,000 rpm. As the polygon mirror 106 reflects the laser beam onto the photosensitive unit 109, a slight inclination of the polygon mirror 106 (which may be caused by wobbling of rotational axis of the spindle shaft) may not reflect the laser beam properly on the photosensitive unit 109 for scanning.
In this sense, the spindle motor for rotating the polygon mirror 106 should rotate very fast and stable in high-degree of accuracy.
However, the spindle motor used for the LBP has a problem of leakage of lubricating oil in the rotational shaft as it rotate very fast in high revolution. The leakage of lubricating oil of the spindle motor may affect the duration of the motor. Further, the leakage of lubricating oil may damage the inside mechanism of the LBP or spoil the printing paper.
FIG. 2 is a cross sectional view of half-side of a spindle motor. The cross sectional view of the spindle motor is symmetry to the half-side view. The spindle motor is basically composed of a rotor 201 and a stator 202. The rotor 201 has a bush 203 pressed to a spindle shaft 204 and fixed with the polygon mirror 106. The rotor 201 is attached to the spindle shaft 204 and the spindle shaft 204 is rotationally attached to the stator 202 by a shaft bearing 205 and a bearing holder 206.
FIG. 3 is a cross sectional enlarged view of inside portion of the surrounding of the spindle shaft 204 and the bush 203 and the bearing holder 206 and the shaft bearing 205. In FIG. 3, a hydraulic pressure 31 presses lubricating oil 30 by the rotation of the spindle shaft 204 and the lubricating oil 30 moves along the surface of the spindle shaft 204 and comes out on the surface of the bush 203. Then the lubricating oil 30 leaks out from a gap portion 32 formed between the bearing holder 206 and the bush 203.
The height of the spindle motor may be shortened by mechanical design of an LBP, which makes the gap portion 32 narrower. In the case that the gap portion becomes narrower, the lubricating oil 30 tends to leak out even more.
Accordingly, in consideration of the above mentioned problems of the related art, an object of the present invention is to provide a shaft bearing structure of spindle motor, including, a rotor rotationally attached to a shaft bearing and a bearing holder fixed on a motor base of a stator, wherein the rotor is fixed with a spindle shaft and confronted with the stator, and the shaft bearing structure is characterized in that an oil cycle material (40, 41) retains and re-flows lubricating oil circulating around the spindle shaft in the shaft bearing, wherein the oil cycle material (40, 41) is placed in the gap between the inner circumference of the bearing holder and the periphery of the spindle shaft, and placed at least contiguous to one edge of the shaft bearing in axial direction of the spindle shaft.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.